Each year fires lead to the loss of large values and many human lives. In the year 2002 the insurance companies in Norway paid out NOK 1.6 billion for fires in houses and 1.3 billion for fires in trade and industry buildings. According to statistics regarding 2001 a total of 65 persons lost their lives in fires in Norway during the year.
9 percent of these fires were caused by heat development in current outlets, switches and fuse equipment. Such overheating may arise in consequence of spark formation, creeping currents in carbonised insulation material or direct series arcs, and mostly well before the circuit is loaded with its maximum current that would result in fuse burning. As electric installations operate today, a traditional fuse in the fuse box will not detect such local overloading or overtemperatures.
Thus, the purpose of the invention is to register or detect and warn with respect to harmful heat development before damage is caused in electric installations or in other places. The invention is not dependent upon the voltage level in an electric installation and will be applicable both in low and high voltage installations. This is obtained by means of the features recited in claims 1-7.
It is previously known to install thermocouples or fuses in electric articles such as hair dryers, extension cord reels and so forth so that the current is interrupted when the temperature rises above a certain temperature limit, in order to protect against overheating. The drawback is that the whole load must flow through the thermocouple or the fuse, and that a series connection introduces junction points which increase the risk of faults occurring.
There is also a risk of a too slow reaction in that often one does not want to break the current or disconnect the voltage at a too early instant, but instead chooses to operate in the border region of what the article or device can tolerate. There is often also included a reset mechanism (“reset button”) for manual resetting. This means that the possible overload may be switched on again, without removal of the cause of the interruption.